The present invention relates generally to a drive recess mold to form a drive recess in the screw head top surface, and more particular to form a novel compound drive recess which permits being driven by various types of drive bit such as slot, Phillips (cross), square, Pozi, and cross-square. In addition, the drive recess formed by this invention also can be driven by its tailor-made drive bit (U.S. Pat. Ser. No. 09/373,022) which gives the compound drive recess the capacity to stand efficient high driving torques with minimal drive bit slip or cam-out.
Currently, conventional screws or bolts with a variety of head types-such as countersunk, oval, pan, truss, etc.xe2x80x94can adapt at least five kinds of drive recesses as shown in FIGS. 1, 2, 3, 4 and 5. A in FIG. 1 is of a slot, B in FIG. 2 a cross, C in FIG. 3 a cross-square combination, D in FIG. 4 a square, and E in FIG. 5 a Pozi. Drive recess structures like above mentioned cannot stand comparatively large torques due to the structure weakness and uneven pressure distribution. Loose fit between the drive recess and the drive bit, which are very common in the above mentioned drive recesses, may produce a large torque causing impaired drive recess or broken drive bit.
A U.S. Pat. No. 4,126,908 titled xe2x80x9cTHREADED FASTENER RECESS FORMING PUNCHCHxe2x80x9d has a double cross-shaped recess mold, so the screw formed by it has a recess in its head as shown in FIG. 5, E of a double cross, limiting available screw drive bits (or screw drive driver). U.S. Pat. Nos. 3,898,706, 4,355,552 and 3,238540 have the same structure shown in FIGS. 3 and 5.
In order to let drive recesses possess the following two featuresxe2x80x94A) stand comparatively large driving torques with high retention of the drive bit; B) enable to be driven by various types of drive bits-the mold for this compound drive recess is therefor devised.
This compound drive recess formed by the present invention consists of four symmetrical fan-shaped portions, a center square portion and eight chamfer edges intermediate the center square portion and each of the fan-shaped portions. Another version of this compound drive recess consists of all the structures except the eight chamfer edges.
Further objects, features and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawing wherein like reference numerals designate like elements throughout the several views.